const_missing oddity?

[Phil Tomson]

def Object.const_missing name
puts "There is no constant: #{name}"
end

irb(main):038:0> Foo { puts "here!"}
NoMethodError: undefined method `Foo' for main:Object
from (irb):38
from :0

irb(main):039:0> Foo
There is no constant: Foo
=> nil

So the block after Foo keeps Foo from being recognized as a constant?
(apparently it's recognized as a method instead)

Phil